Courtly Provocateur might be cool in here, not a zombie, but sick combo with Vedalken Ghoul. Could even use it to ramp Diregraf Captain ability to kill some of your tokens you are making and just make your opponent lose life. Or just make your opponents run into your death touch creatures.

Possible sideboards for flying decks: Geralf's Masterpiece, Gloomdrifter, Skaab Ruinator

instead of Diregraf Ghoul in side board, check out Dread Wanderer

Compelling Deterrence Never really thought about how good this could be with Black/Blue Zombies.

+1

I would definitely try to drop down on all of these 3 drops. I'm sure it makes it incredibly hard to play multiple spells a turn and you're not doing a whole lot until you hit 3 lands. I would lower the curve considerably. I would stick with one play set of Zombie lords with the Warchiefs. Undead Augur or Cryptbreaker will help you with card draw. And I would look for beaters that's come in the 1 and 2 mana slots like Champion of the Perished or Tainted Adversary

Cool deck, get Training Grounds for sg’s ability.

Awesome decklist! Definitely want to try this out!

Call to the Grave was a staple in my Type 1 deck about 20 years ago. I dunno, might be good here too even after all these years.